Cellulose nanocrystal composites with enhanced mechanical properties for robust transparent thin films

Cellulose is attracting increasing interest as a sustainable technological material, owing to its unique combination of properties, such as abundance in nature, biodegradability, nontoxicity, cost effectiveness, and good mechanical properties. Here, we developed composite thin films based on carboxymethylcellulose (CMC) reinforced with TEMPO-oxidized cellulose nanocrystals (TOCNCs). The strength and stiffness of the CMC/TOCNC nanocomposite film increased by ∼400% and ∼20%, respectively, compared to pure TOCNC films, while preserving the deformation capability of pure CMC films, the latter being less stiff, but more ductile than pure TOCNC films. We demonstrated the tunability of the CMC/TOCNC self-assembly, through Fe3+ complexation, resulting in transparent cross-linked nanocomposite films with enhanced strength (163.5 ± 51.3 MPa) and stiffness (Young’s modulus of 14.5 ± 4.0 GPa), with no significant loss in strain at failure (2.8 ± 1.1%). Finally, as applications of newly developed films require durability in realistic operating conditions, which do not involve static forces only, we tested our films against loading–unloading cycles, demonstrating robust and stable performance. By enabling a deeper understanding of the fabrication process and mechanical properties of cellulose-based nanocomposite films, this work expands their potential applications across a broad range of fields, from environment-related processes, such as decontamination, to the biomedical field.